Terroir

Climate and Weather

Climate is determined by the amount of sunshine, heat and rain that a region consistently receives on an annual basis. Weather is the vintage variation from year to year and also includes unfortunate meteorological events such as frost or hail.

Temperature and sunlight are central in determining wine quality and style, because sunlight enables photosynthesis and temperature determines respiration. In hotter, sunnier climates, grapes produce wines with fuller body, higher alcohol and lower acidity. Temperature after veraison, or the moment when grapes change color and begin to ripen, is particularly important since insufficient temperature during ripening will produce wine that is lean, austere and lacking in fruit and body. For example, Cabernet Sauvignon ripens fairly late and in cooler climates it can produce thin, acidic wines without proper fruit development.

In general, the more consistent the temperature, the more consistently grapes will ripen. This lack of fluctuation is referred to as equability. Two factors that aid equability are proximity to large bodies of water and thermal inversion created by the slope of the hills on which the vineyards are planted. Finally, the temperature swing between winter and summer also influences quality. Late-ripening grapes, such as Cabernet Sauvignon, do not tolerate a sudden drop in autumn temperature very well and can produce herbaceous, unripe grapes as a result.

Grapes ripen as a result of photosynthesis, the binding together of water and CO2 from the atmosphere to form starch. This is accomplished with the help of light energy from the sun absorbed by chlorophyll in the vine and leaves. Ultimately, a vine needs both sunlight and warm temperatures for the fruit to ripen effectively.

Respiration takes place at the same time as ripening. During respiration, oxygen combines with the sugar from the vine and with other compounds, including amino acids and organic acids, releasing carbon dioxide. Respiration is the opposite of photosynthesis and vines respire more sugar in warmer weather, although the rate of photosynthesis remains the same.

The amount of rain and the time of rainfall during the growing season are important elements of climate. Rainfall is particularly important in areas where irrigation is not allowed, as is the case in much of Europe. In general, cool climates require at least 500 mm/yr of rain to produce wine grapes, while warmer climates need 600–750 mm/yr. Rainfall is less important in regions where irrigation is permitted, but ill-timed rain can still ruin a harvest or have a dramatically adverse effect on the quality of the wine.

Weather or annual variation in climate is a fixation of wine lovers. Warm, mild temperatures at bud break can give the vines an early start, while the same type of weather at flowering can lead to a bigger crop because pollination of the vines will be more consistent. Warmth and sunshine during ripening leads to lush, rich wines. Dry weather at harvest allows the vine to ripen and helps the bunches avoid rot and dilution. Late season hailstorms can devastate ripe grapes as can ill-timed frosts.

The date of first and last frost play a role is determining quality. Some grapes bud early, and are therefore ill-suited to climates prone to late frosts. Others ripen late and can have difficulty ripening in regions that have early frosts in the fall. When the buds are particularly tender in the spring, frost damage can severely limit yield and quality.